Date | November 2018 | Marks available | 2 | Reference code | 18N.3.sl.TZ0.7 |
Level | SL | Paper | 3 | Time zone | TZ0 |
Command term | Deduce | Question number | 7 | Adapted from | N/A |
Question
Lipids play several roles in our bodies.
A phospholipid generally consists of two hydrophobic fatty acids and a hydrophilic group.
Fatty acids are products of the acidic hydrolysis of phospholipids. Deduce the names of the other two products.
The iodine number is the maximum mass of iodine that reacts with 100 g of an unsaturated compound.
Determine the iodine number of stearidonic acid, C17H27COOH.
State two functions of lipids in the body.
Outline one effect of increased levels of low-density lipoproteins in the blood.
Markscheme
phosphoric acid ✔
glycerol/propane-1,2,3-triol ✔
Do not accept formulas.
ALTERNATIVE 1:
4 C=C bonds/4 carbon to carbon double bonds ✔
mass of iodine per mole of acid = «4 × 253.80 g mol–1 =» 1015.2 «g mol–1» ✔
iodine number «= » = 367 ✔
ALTERNATIVE 2:
4 C=C bonds/4 carbon to carbon double bonds ✔
« =» 1.447 mol of I2 «reacts with 100 g» ✔
iodine number «= 1.447 mol × 253.80 g mol–1» = 367 ✔
Award [3] for correct final answer.
Any two of:
«structural» components of cell membranes ✔
energy storage/utilization ✔
«thermal/electrical» insulation ✔
transport «of lipid-soluble molecules» ✔
hormones/chemical messengers ✔
Accept other specific functions, such as “prostaglandin/cytokine/bile acid synthesis”, “cell differentiation/growth”, “myelination”, “storage of vitamins/biomolecules”, “signal transmission”, “protection/padding of organs”, “precursors/starting materials for the biosynthesis of other lipid”.
Any one of:
atherosclerosis/cholesterol deposition «in artery walls» ✔
heart/cardiovascular disease ✔
stroke ✔
Accept “arteries become blocked/walls become thicker”.